Organic materials, whether natural or synthetic, are conventionally protected against degradation by oxidation and by ultraviolet light and/or heat by incorporating a stabilizer in the materials. The choice of a stabilizer depends upon what particular source of degradation is to be countered, the type of material in which the degradation occurs, and the proposed length of time for which protection is sought under expected conditions.
This invention is particularly directed to the protection of organic materials against degradation by oxidation at temperatures below about 200.degree. C. for relatively short periods of time, and at ambient temperatures for extended periods of time. The compounds of this invention belong to a well-recognized class of antioxidants termed hindered phenols`, which as the term implies, possess an OH group which may be either partially or totally hindered by adjacent substituents on the phenol molecule. Compounds which serve as antioxidants are disclosed in Atmospheric Oxidation and Antioxidants by Gerald Scott, Elsevier Publishing (1965); Antioxidants Syntheses and Applications by Johnson, J. C., Noyes Data Corporation (1975); and other publications.
Much work has been done in this art, and much has been written to explain the complex chemical reactions which occur when a material loses its structural integrity, flexibility or resilience, or becomes discolored. Much has been written to account for the stabilizing effects of hindered phenols, and the probable mechanisms by which these occur. Despite all the work and teachings related to it, the simple fact is that the stabilizing action of hindered phenols is unpredictable.
Recognizing that most of the major developments in this field have been the products of a well-directed empiricism, and further, that the synthetic polymer industry has absorbed much of the teachings from the rubber industry where hindered phenols have long been favored, it is nevertheless surprising that four (4) hindered phenol moieties may be linked to form a cyclic compound which has the best characteristics of the most effective hindered phenols even when used in different media. As those skilled in the art are well aware, stabilizers which are effective in natural or synthetic rubber are usually ineffective in other synthetic resinous materials.
Some examples of phenolic antioxidants are 2,6-di-t-butylphenol; 2-methyl-4,6-dinonyl phenol; 2,6-di-t-butyl-p-cresol; 2,2'-methylene-bis-(4-methyl-6-t-butyl phenol); 1,1'-methylene-bis-(2-naphthol); 4,4'-methylene-bis-(2,6-di-t-butyl phenol); 4,4'-thio-bis (6-t-butyl-m-cresol); and the like. Although any phenolic antioxidant used in combination with the substituted metacyclophanes would improve the heat and oxygen stability of the compositions the more preferred phenolic antioxidants are those having alkylhydroxyphenyl substituents on an ester or a heterocyclic nucleus.
Particular examples of phenolic antioxidants having alkylhydroxyphenyl substituents on an ester nucleus are compounds disclosed in U.S. Pat. No. 3,330,859 exemplified by di-lauryl .alpha.,.alpha.'-bis(3,5-di-butyl-4-hydroxybenzyl)malonate; and disclosed in U.S. Pat. No. 3,627,725 exemplified by tetrakis (methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate) methane; and the like.
Examples of phenolic antioxidant compounds having alkylhydroxyphenyl substituents on a heterocyclic nucleus are compounds where the heterocyclic nucleus is a triazine nucleus such as compounds disclosed in British Pat. No. 977,589 and exemplified by 2,4,6-tris(4-hydroxy-3,5-di-t-butyl benzylthio)-1,3,5-triazine; compounds disclosed in U.S. Pat. No. 3,706,740 and exemplified by 2,4,6-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)-1,3,5-triazine; disclosed in U.S. Pat. No. 3,567,724 and exemplified by hexahydro-1,3,5-tris[3,5-di-t-butyl-4-hydroxyphenyl) propionyl]s-triazine; disclosed in U.S. Pat. No. 3,694,440 and exemplified by 1,3,5-tris(4'-hydroxy-3',5'-di-t-butylphenylpropionyloxyethylthiopropionyl )hexahexahydro-1,3,5-triazine; and the like.
Examples of phenolic antioxidant compounds having alkylhydroxyphenyl substituents on an isocyanurate nucleus are compounds of the formula disclosed in U.S. Pat. No. 3,531,483 and exemplified by tris-(3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate; disclosed in U.S. Pat. No. 3,678,047 and exemplified by 2,2'2"-tris(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy)ethyl isocyanurate; and the like.
Still other hindered phenols useful as thermal antioxidants are disclosed in U.S. Pat. Nos. 3,920,659; 4,069,195; and 4,326,061 which are incorporated herein by reference as if fully set forth.
It is known that p-t-butylphenol and formaldehyde, when base-catalyzed, yield a series of cyclic compounds made up of tetramers, bishomooxa tetramers, octamers, and the like, which have been the subject of a detailed investigation, reported in a series of articles one of which is Calixarenes. II. The Isolation and Characterization of the Calix [4]arene and the BishomooxaCalix[4]arene from a p-t-Butylphenol-Formaldehyde Condensation Product, by Gutsche, David C. et al, Tetrahedron Letters, No. 24, pp 2213-2216 (Pergamon Press Ltd., 1979). These compounds, when appropriately functionalized, have the ability to form complexes which are enzyme model candidates. As will immediately be evident, these calixarenes have their OH groups within the `main ring`, that is, the ring formed by the plural butylphenol molecules, and the condensation reaction occurs under base-catalyzed conditions, while the synthesis of this invention, as described hereafter, is non-catalyzed. It will also be evident that formaldehyde (normally available as an aqueous solution) and paraformaldehyde (normally a solid consisting essentially of polymers of formaldehyde) behave quite differently even if they are related compounds.